Controls for electrical string instruments



April 13, 1965 c. R. EVANS 3,178,501

CONTROLS FOR ELECTRICAL STRING INSTRUMENTS Filed May 16. 1961 3 Sheets-Sheet 1 PIEZOELECTRIC PICK-UP INVENTOR CHA UNCEV RICHARD EVANS Fl 5. El

BY 84%, om, fluzufid, Jmym ATTORNEY 8 April 13, 1965 c. R. EVANS 3,178,501

CONTROLS FOR ELECTRICAL STRING INSTRUMENTS Filed May 16. 1961 3 Sheets-Sheet 2 PIE ELECTRIC ?J. E E:

INVENTOR CHAUNCEY RICHARD EVANS F 1.5.7

BY 78%, 9m, fimalei; ATTORNEYS April 13, 1965 c. R. EVANS CONTROLS FOR ELECTRICAL STRING INSTRUMENTS Filed May 16. 1961 3 Sheets-Sheet 5 OOOON INVENT OR CHAUNCEV RICHARD E VANS BY 7 1 fl pam, fiance/lat, Ju/ww ATTORNEYS United States Patent 0 3,178,501 CONTROLS FOR ELECTRICAL STRING INSTRUMENTS Chauncey Richard Evans, Salt Lake City, Utah, assignor to Atuk Corporation,'Salt Lake City, Utah, a corporation of Utah Filed May 16, 1961, Ser'. No. 110,483 1 Claim. (Cl. 841.14)

This invention relates to controls for electrical string instruments, and more particularly to tone controls and volume controls formusic systems of the type that includes a string instrument, a piezoelectric pickup for converting the mechanical vibrations of the string instrument into electrical pulses, an amplifier, and a loud speaker unit.

It long has been recognized that the quality of the music produced by a string instrument is affected by the room in which the instrument is played. The acoustical qualities of some rooms are such that the low frequency components of the music,-that is the bass tones, are unduly emphasized. This is particularly serious in connectionwith theplaying of instruments such as the classic guitar, where the artist usually finds it diflicult to giveproper emphasis to the higher tones even under the most favorable environmental circumstances.

This difliculty is overcome in accordance with thepresent invention, by the provision of a simple control adapted to be located in a position where the musician may manipulate it conveniently. The controloperates to vary the magnitude of the low frequency signals fed to the amplifier unit, so that, if the room tends to accentuate low frequency tones, the musician may compensate for this tendency by deemphasizing these components prior to amplification.

It has been observedthat' the frequency response characteristics of piezoelectric pickups vary with the external resistance loads in the transducercircuits. When the load resistance is high, the system responds with reasonable vniformity to all frequencies in the audio range. However, if the load resistance is reduced materially, the system will discriminate against the lower frequencies.

The tone control of the present invention makes use of'this phenomenon. It is a variable resistance'connected across a piezoelectric pickup. By varying this resistance, the artist may obtain the degree .of low frequency discrimination that-best counteracts the low frequency accentuation characteristics of the room in which he is playing.

Another problem always present in the, use of music systems of the type with which this invention is concerned is that of volume control. At one moment, the artist may be rendering a solo or accompanying a vocalist. At the next moment, he may be required to play with a large group of other instruments. As will be apparent, these different situations require different output levels if the mostdesirable results are to be attained. The present invention recognizes these difficulties and provides for the location of effective volume control elements at points Where they can be operated conveniently by the musician.

In a preferred embodiment of the invention for use with a classic guitar, both tone control and volume control components are disposed within a novel foot rest that may be used in place of a stool of the type heretofore used by classic guitarists. This location of the manipulatable elements ofthe controls makes it possible for the artist to adjust them from time to time Without distracting the audience and without materially altering his position.

This embodiment of the invention incorporates two volume controls. Oneof them may be set so as to establish a volume level suitable for vocal accompaniment work, while the other may be set so as to establish a suitable level for work with a large dance band, for example. It is particularly desirable also that the system include means that will permit the musician to shift quickly from one pro-selected volume level to another pre-selected volume level. To this end, the control of this invention includes a switch that permits the musician to inactivate one or the other volume control elements of the system at will.

In another embodiment, the invention takes the form of a variable resistance mounted directly on the bridge of a bass violin. This simple control is effective, convenient to use, and very inexpensive.

These embodiments of the invention are illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a music -system.ineluding a classic guitar, a foot rest control unit in accord ance with the present invention, and a loud speaker enclosure;

FIG. 2 is an elevational view of a piezoelectric transducer used to generate electrical pulses from the mechanical vibrations of a string of the guitar;

FIG. 3 is a diagram representing the electrical characteristics of a circuit including a transducer of the type shown in FIG. 2;

FIG. 4 is a chart indicating the frequency response characteristics of a piezoelectric pickup under different conditions of external loading;

FIG. 5 is a circuit diagram for a part ofthe. system of FIG. 1, showing the control features characteristic of the present invention;

FIG. 6 is an elevational view of a bridge for a bass violin incorporating the present invention;

FIG. 7 is a partial cross sectional view taken along the line 77 of FIG. v6; and

FIG. 8 is a circuit diagram for a system incorporating a control unit or" the typeshown in FIGS. 6 and 7.

In FIG. 1, there is shown a classic guitar It) that may be of. any desired construction. It includes strings 12 and a piezoelectric bridge unit 14 preferably ofthe type disclosed in my co-pending application, Serial No. 28,567, filed 'May 12, 1960. The piezoelectric bridge unit 14 serves as a pickup for converting the vibrations of the strings 12 into electrical signals.

From the guitar It? the electrical signals pass along a lead 15 to a foot rest control unit 16, the electrical characteristics of which will be described in greaterv detail with reference to FIG. 5. 'From FIG. 1, it will be observed that the foot rest unit 16 is provided with suitable legs 18 and is of a size such that it will accommodate the foot of the musician.

The classic guitar usually is played by a musician seated in a chair with one foot resting on a foot stool so as to elevate the upper portion of his leg properly for supporting the guitar body. It is intended that'the foot rest control unit 16 shown in FIG. 1 be used in place of the conventional stool used in this type of work.

After being modified, if desired, in the control unit'id,

U the electrical signals pass on through a line 20 to an amplifier and related equipment disposed Within a loud speaker enclosure 22. The components within the enclosure 22 form no part of the present invention and they may be conventional.

Referring now to FIG. 2, the piezoelectric bridge 14 is made up of a group of barium titanate transducers 24 supported on a base member 26. The strings 12 bear against the transducers 24 in such a Way that the vibrations of the strings 12 result in pressure variations in the barium titanate. These pressure variations cause differences in electrical potential between the inner and outer surfaces of the barium titanate transducers 24. A more complete disclosure of a piezoelectric bridge unit of this type is contained in my prior application identified above and reference may be had thereto if desired.

The barium titanate material acts as a generator, and it also has internal capacitance and internal resistance. These qualities are suggested diagrammatically in the equivalent circuit of FIG. 3. This circuit may be thought of as comprising a generator 28, a capacitance 3t corresponding to the internal capacitance of the transducer, and a resistance 32 corresponding to the internal resistance of the transducer. In a typical barium titanate transducer of the type used in the present invention, the internal capacitance 30 may be about 280 micro-microfarads. The internal resistance of such a unit is very, very high, and for purposes of the present invention, there is no need to evaluate it precisely.

FIG. 3 also depicts an external load resistance 34. This has been shown as a variable resistance, and it will be evident that the actual magnitude of the signal developed by the transducer will depend upon the magnitude of this resistance.

It also has been discovered that the frequency response characteristics of the circuit of FIG. 3 vary with the magnitude of the external load resistance 34. This has been shown graphically in FIG. 4.

The individual curves in FIG. 4 represent the frequency response characteristics of the circuit of FIG. 3 for particular settings of the variable loading resistance 34. For example, curve a represents the conditions that result from the use of an external resistance of .015 megohms (l5 kilohms), while the curve b represents the conditions that result from the use of an external resistance of megohms.

It should be noted that, when the external loading resistance is very high, the circuit responds uniformly to all frequencies within the audio range. However, as

the external resistance is decreased, the lower frequencies are attenuated more and more. Thus, the variable external resistance 34 may serve as a tone control. By varying this element, the musician may eliminate or deemphasize the low frequency components of the electrical signal from the pickup when he desires.

Such a control is more useful in compensating for the bass characteristics of certain rooms. In many spaces where music is played, low frequency sounds are emphasized by resonances in the room and high frequency sounds are absorbed or attenuated by the draperies and other furnishings. As a result, the tonal content of the music actually heard by the audience is somewhat different from that created by the musician. The dilficulty can be overcome to some extent by using the tone control of this invention to deemphasize the low frequency components of the electrical signals generated by the artist.

The foot rest control unit 16 of the system shown in FIG. 1 includes a tone control of this type. Referring to the wiring diagram shown in FIG. 5 for the foot rest control unit 16, it will be seen that the resistances 36,

. 38, 40, 42 and 44 cooperate with a selector switch 46 to provide a variable load for the piezoelectric pickup. With the switch 46 in the position shown, the resistances 38, 40, 42 and 44 are in the pickup circuit, but movement .of the switch 46 in a clockwise direction to the next stop or terminal will eliminate resistance 38 from this circuit, etc.

A set of values that has been found to be suitable for the tone control resistances is as follows: Resistance 36, 680 kilohms; resistanace 38, 220 kilohms; resistance 40, 220 kilohms; resistance 42, kilohms; and resistance 44, 47 kilohms.

The foot rest control unit 16 also includes a volume control shown in FIG. 5 as a series of resistances 48, 50, 52, 54, 56 and 58 cooperating with selector switches 60 and 62.. The signal from the tone control may pass to the volume control by way of an on-off switch 64 that permits the musician to disconnect the electrical output entirely so that the only sounds produced are those generated acoustically in the guitar itself.

A two-position switch 68 makes it possible to connect either the selector switch 60 or the selector switch 62 to the line carrying the output signal to the amplifier of the system.

In using the equipment, the musician normally actuates the selector switches 60 and 62 before commencing his performance. For example, he may adjust one of the switches, say that designated by the numeral 60, to give a volume suitable for vocal accompaniment, and he may adjust the other of the switches 62 to give a volume suitable for rhythm work with a dance hand. Then during the performance, the musician may manipulate the twoposition switch 68 to shift quickly and easily from one pre-selected volume level to another in accordance with the requirements of the moment.

Suitable values for the resistance units of the volume control are as follows: Resistance 48, 680 kilohms; resistance 50, 470 kilohms; resistance 52, 330 kilohms; resistance 54, 180 kilohms; resistance 56, kilohms; and resistance 58, kilohms.

Preferred locations for the various manipulatable elements of the foot rest control unit 16 are indicated in FIG. 1. The selector switches 46, 60 and 62 may be controlled by rotatable knobs 46a, 60a and 62a, located on one side of the foot rest. The on-off switch 64 and the two-position switch 68 may be conventional snap switches actuated by levers 64a and 68a located on the opposite side of the foot rest.

Another music control utilizing features of the present invention is disclosed in connection with FIGS. 6, 7 and 8. FIG. 6 illustrates a bridge 70 for a bass violin. The bridge 70 may be similar in overall shape and size to the conventional bridges, but it is provided along its upper surface with piezoelectric transducers 72 for receiving the strings of the instrument.

As shown in FIG. 7, a recess 74 is formed in One surface of the bridge 70 for receiving a variable resistor 76. A rotatable shaft 78 extends laterally from the variable resistor 76 through an opening 80 in the bridge 70 to a control knob 82 on the opposite face of the bridge 70. Rotation of the control knob 82 will vary the resistance of the variable resistor 76.

The resistor 76 may be held in position by a body of insulating plastic material 84 molded in place so as to fill the recess 74 and to cover adjacent portions of the face of the bridge '70. This plastic material 84 covers and protects leads 86 extending downwardly from the outer surfaces of the transducers 72 to the resistor 76. The inner surfaces of the transducers 72 also are connected to the resistor 76 by means of leads 88 extending downwardly through apertures in the bridge 70. A long lead 90 carries the output signal from the resistor 76.

As shown in FIG. 8, the resistance element 76a of the variable resistor 76 is connected across the terminals of the piezoelectric pickup and the movable element 78a thereof is mechanically connected to the control shaft 78 and electrically connected to the output line 98a leading to the amplifier of the system. This arrangement provides a volume control located so as to be of maximum usefulness to the musician.

Although two embodiments of the invention have been illustrated and described in detail, it is recognized that various other changes and modifications will be obvious to persons of ordinary skill in the art. It is intended, therefore, that the foregoing description be considered as exemplary only and that the scope of the invention be ascertained from the following claim.

I claim:

In a music production system of the type having a musical instrument, a piezoelectric transducer for converting mechanical vibrations in the musical instrument into electrical signals, means for amplifying the electrical signals, and loud speaker means for converting the electrical signals into acoustic energy, the improvement which comprises a control unit including a variable load resistance connected across the output from said transducer to provide a tone control, a second resistance connected in parallel with said variable resistance, first selector means for receiving the voltage signals appearing at various points along said second resistance, second selector means operating independently of said first selector means for receiving voltage signals appearing at various points along said second resistance, and a switch for connecting either said first selector means or said second selector means to said amplifier.

Reterences Cited by the Examiner UNITED STATES PATENTS 502,944 8/93 Zender 84-232 1,242,633 10/17 Allen 84-232 1,915,858 6/33 Miessner 841 2,222,057 1 1/ Benioff 84-1 2,279,500 4/42 Severin et a1 179-100 2,486,264 10/49 De Armond 84-1 2,494,485 1/50 Notara 84-1 2,625,849 1/53 Melita 84-309 2,770,158 11/56 Bowman 84-309 2,964,985 12/60 Webster 84-1 3,115,588 12/63 Hueter 310-8 FOREIGN PATENTS 256,865 3/49 Switzerland.

ARTHUR GAUSS, Primary Examiner. LAWRENCE V. EFNER, Examiner. 

